Electrical discharge lamp



y 13, 1952 H. E. KREFFT ELECTRICAL DISCHARGE LAMP 2 SHEETS-SHEET 1 Filed D60. 4, 1948 INVENTOR HERMANN EDUA KREFFT ATTORNEY May 13, 1952 KREFFT 2,596,697

ELECTRICAL DISCHARGE LAMP Filed DGC. 4, 1948 2 SHEETS-SHEET 2 INVENTOR HERMANN EDU RD KREFFT BY M ATTORNEY meterito; several .1 millimeters.

Patented May 13, 1952 UNITED STATES PA NT ELECTRICALDISCHARGE LAMP i v Hermann Eduard Krfit, Buenos Aires; Argentina Applica'tionDecember 4, 1948, Serial No. 63,570: In Switzerland December 8, 1947 I a'dlai ins. (01.31%26) The present invention relates to electrical discharge lamps and more particularly. to high pressure electrical. discharge lamps. I

The modern developmentof mercury high pressure lamps has resulted in the production of --lamps having increased vapor pressuresup to very high values of the order of a hundred atmosn e es I I Under these very high pressures, the gradient ofthe arc obtains values of 100 to500 volts per centimeter; andthe electric power dissipated per unitarc-volume is very considerable! Owing .to this fact, the brightnessof the arc, depending Ionthedegree of the electrical power applied, amounts'from 10,000 to 100,000 candles per square centimeter. In the ultra-violet and infra-red, a radiation corresponding to this high brightness also: exists.- The radiant eiiiciency in I these spectral ranges is very considerable and, forexample, aluminous efficiencyof 50 to 70 lumens per watt is obtained. Because of these properties, the super high pressure lamps find an extremely wide'field of applications in all branches-of lighting and *uses of radiation. I I

Onaccount ofthe great strain-produced by pressure and temperature,- the discharge, tube of these; lamps usually consists of a thick-walled quartz-glass of spherical shape and of such surface; dimensions; that. in operation it acquires temperatures of about 800" C. to 1000 The electrodes. of such. lamps are; arranged close to each. .other,-. so that-the length of-the, are. dependingomthe'type of. the lamp and the power consumed, amounts from a .few tenths of. a milli- The discharge tube. generally contains a: limited quantity of mercury to which cadmium,.zine or thallium may be added, and which under: full operationof the 1a1nps,:is completely evaporated. Super high pressure lamps: of the: same construction are filled, .instead of with mercury; with krypton. or xenon:under highpressureof about 20" atmospheres, thereby becoming lamps-50f high brightne'ss. andefliciencyand which. are particularly adapted to operationiwith"condenser discharges. Lamps of thekin d above describedhave been madezup to now for an inputo fabout 50. watts to 2000;: watts;

These-super; high pressure lamps have not been; used" hitherto to an extent corresponding to their eificiency and the great variety oi-uses they may. find, for the reason that their use has been; limited by. various disadvantages. It iss'd mqlllt to.- connect asbase to these lampsbe- .causeithe uartz bulb andv-the-seals acquire "high 2 temperatures. In order' to utilise optically their high brightness,- bases which-are accurately made must be used and carefully adjusted to the lamps. Furthermore, quartz-glass is very susceptible to contamination which causes; devitrification; and thuslowers opticalefficiency and lamplite, In order to avoid these drawbacks thelamps have been often supplied, :in a; manner already known, with an outer glas's'jacketa However, the diffi lty. Qt u a e. bas nais n t e m nat d" in this, w urt e mp t chacket i n t re e QP QQ -W FS I an r eu e ov e ing ofthe quartz tube when givensmall dimensions. Above all,. the; use of these-lamps are handicapp-edby occasional; explosions of the quartz bulb which endangernearby persons or u ment t 1501 Object t i nv nti n. t r v de an le a s h lamp er efe: op t under very high pressures It is another object of this invention to provide an eleetricaldischarge lamp which has a great flexibility; of use in thatnovel modifications enable its applican o her euti usesr lum li o,- jection, fluorescence analysis et'c, ltisa furh r object um -in io tqpr v d n e e r a d s h e l p f r, upe h h. re discharges. Other objects and advantages of this invention will become apparent from the description hereinafter following-and the drawings rorming part h ereo f in which:

I Figure 1 .is a schematic representation of an electrical.d-ischargelamp and envelope therefor according to. thepresent invention, II I Figure 2 is a schematic'representationof' a super high pressure 1 electrical discharge lamp and envelope, therefor, I. r I II Figure 3 ;illustrates a modification of the present invention,

Figure. i is a schematic representation of an electrical discharge-lamp Qf the presentdnventionincluding, an auxiliary: electrode therefor and a modification of the reflector surface; and

Figure; 5 illustrates another'modification of the present invention, I V I I According; to the present invention, thedisadvantages of mercury high pressure lamps here- .inbefore set forth are avoided. if thehigh pressure lamps, subsequently referred to as"tubes-,"

are arranged within. a comparatively-wideand thick-walled container, formed by two shells, made of pressed glass, which serves as a'reflector, which modifies the composition of radiations, which protects surroundingiobjects againstd'am ages caused. by. explosion, and which" facilitates lamp. The light transmitting shell is given a suitable curvature adequate to the pressure of the surrounding atmosphere. The rims of both shells are fused or soldered to each other as far as this is possible in glasstechnology; In other cases, they are firmly connected to each other by.

mechanical means.

Reflector-lamps of the kind described are already known in combination with incandescent filaments as source of radiation, and they are widely used because of the optical advantages connected with this construction. Considering the brightness ofsuper high pressure lamps, which is to 100 times larger, anaccurate optical-adjustment of the arc is of still greater importance .for the utilization of its high brightness and for the production of a definite path of the beam emitted. Consequently,thelamp, according to the present invention, is particularly adapted to the construction of searchlights of' high optical efficiency which can be used also as ultra-violet and infra-red searchlights. In automobiles, the new lamp improves the performance by pressing in a mold. This method of production has the additional advantage that the thickness of the glass through which radiation passes can be always given exactly the value required and, consequently, the lamps always have the" same spectral distribution of radiation, which for instance for medical uses, is of great importance for accurate dosage. The wall-thickness of the molded shell, which is comparatively large, is of no disadvantage for lamps of this kind as the ultra-violet spectrum can be given an accurate short wave limit, or visible radiation can be entirely eliminated, when a wall-thickness of a few millimeters is used. Owing to the particular of headlights, up to now operated with incandescent filaments, many times, as the arc has at least ten times the brightness, three times the efficiency, and a spectral composition of radiation more favorable for the use of polarization filters.

Various other constructions and uses will be indicated in the following description.

As super high pressure discharges also are excellent sources of ultra-violet radiation, they find a wide field of application in therapeutic lamps, in lamps --for fluorescence analysis and other technical uses of ultra-violet radiation, and,

also, as germicidal lamps. In these applications, a well defined spherical distribution of radiation, i. e. the quantitative reproducibility in different lamps of one type, plays an important role as their use, for example, the dosage in therapeutical applications, is greatly simplified in this way. For these uses, the shell through which radiation emerges must-possess a' special and well defined transmission which theor'dinary technical glasses generally donot h'ave. The reflector shell can be madeofordinary glasses in all cases,'while the special glasses, which in most cases are hard to produce and to work, need only be used for the other shell. For ultra-violet therapeutical lamps, this special glass should have as high an ultra-violet transmission as possible and it should cut oif the spectrum in a definite and reproducible manner. In lamps for fluorescent analysis, it is desirable to exclude visible radiation entirely and to utilize ultra-violet radiation or narrow ranges of wave-length of this radiationonly. These special glasses must be made from pure materials and they are frequent- 1y produced under special conditions. Their composition mostly differs from that of ordinary glass and'they are hard to work. Therefore, it is a great advantage of the lamps of the present invention that only the shell in the path of the emerging radiation has to be made with these special glasses, and that this hell is produced composition of these special glasses, it is frequently not possible to fuse the two shells to each other even when the material of the reflector shell is adapted to the composition of the special glass. In these cases, it is sufficient to connect firmly the rims of the shells by mechani-- cal means and, consequently, the space between the shells cannot 'beevacuated, which is not absolutely necessary as the tube is not. susceptible to oxygen. In some cases, the transmitting shell may consist of 'press'edquartz-glass or of a glass similar toquartz with high ultra-violet transmission. 7 r l Reflector lamps containing a high pressure or super high pressure tube within an outer envelope, which serves as reflector, are already known, but in this. type of lamps the envelope is blown in the mold like a bulb, and the tube is mounted on a lamp stem in the usual way. It is not possible, however, to accurately reproduce the wall-thickness of the envelope made in this way and to give it a thickness of 'a-few millimeters. Furthermore, only such glasses can be used which can be blown in the mold and sealed to the stem. Frosting and application of the reflecting material to the bulb is very diflicult. Particularly, it is almost impossible to mount the tube exactly. in the required position with respect to the reflector. In comparison with the lamps which are already known, the lamps made according to the present invention, therefore,

are a great improvement.

The arrangement of a super high pressure tube in a container consisting of two molded shells is ments mayoccur, all damage to'nearby objects can be avoided when the reflector is protected by means of a metallic shield, while the trans mitting shell is protected through a wire screen arranged between this shell and the tube, or by a screen imbedded'in the light transmitting glass and thus preventing total destruction.

During manufacture of the new lamps, two reflector shells provided with conductors and an exhausting tube, the rims of which are suitably ground, make a close fit and are put together tightly. The space enclosed by the reflector shells is highly evacuated. A piece of metal, e. g.

aluminum, which is contained in a tungsten coil fastened'to the conductors, 'is' evaporated by heating the coil. Having been supplied with a reflecting layer in this way, the shells are separated and the tube is mounted on the supports by means of a'gaugewhich provides for the'exact position of thetube with respect to the reflector. Ifa-non-specularreflecting layer is to be made, the surface of the shell is frosted chemically, or by sandblast, before the metallic layer is applied. In this case, the inner surface of the other shell is also frosted. This frosting of the surfaces is of importance for lamps with broad spherical distribution of the radiation; the degree of frosting, however, must be accurately reproduced if the lamps are to have identical optical properties. After the mounting of the tube corresponding pairs of shells are fused to each other at the rims. The shells are carefully annealed and the rims are fused to each other by means of a pointed flame. The container is finally evacuated and filled with nitrogen or a rare gas. The pressure of the gas is preferably kept low enough to prevent an inner pressure exceeding atmospheric pressure during operating of the lamp, which may cause an explosion in case the tube happens to break. When the shells are madeof two different glasses, it is advantageous to connect them to each other by means of a soft glass enamel. When this. methodxcannot be used on account of too large diiferences in glass properties, the rims may be fastened to each other, in a way already known, 'by means of a soldering metal, or a vacuum proof connection is altogether given up and the shells are pressed against each other by a metal ring enclosing the rims and tightly pressing them together.

Some lamp constructions, made according to the invention, are contained in the attached drawings, which show different types of lamps according to the different uses of these lamps.

Figure 1 shows a construction suitable for illumination, or for medical uses. The tube I, which is made of quartz-glass, in this case has a power dissipation of 300 watts. Its discharge vessel, which is nearly spherical, has an outer diameter of about 20 millimeters and the thickness of the wall amounts to about 2.5 millimeters. It is supplied with electrodes 2 consisting of tungsten wire or small bodies of sintered tungsten which are suitably activated with thorium oxide,.or thorium, and which are about three millimeters apart. Instead of tungsten, I may use any other suitable refractory metal or in place of thorium or thorium oxide, I may use any other activation material, whether in the form of metal or in the form of oxide, to produce the activated electrode. The electrodes are mounted on seals 3 containing leading-in conductors, which are fused to the envelope. A

tight connection between the quartz-glass of the a rare gas of about 20 millimeters pressure or other pressure, lower or higher, suitable for starting a discharge, and an accurately determined quantity of mercury which, under operation of the tube and when completely evaporated, produces a pressure of about 40 atmospheres. Under these conditions, when the electrodes are connected to a line of 110 to 220 volts in series with a choke or resistance of suitable size, an arc is produced between the electrodes which has a brightness of about 30,000 candles per square centimeter and an intensity of about 2,000 candles. The voltage drop of the arc is, about 80 volts. The tube is mounted within a container formed by the molded shells 4 and 5. The shell 4, which serves as reflector, has a paraboloid shape while the shell 5 through which the radiato the pressure of the surrounding atmosphere.

To the shell 4, pins 6 are tightly fused by means of metallic rings 1. The pins support the lamp in the lamp-holder and also serve as leading-in conductors. Furthermore, they carry supporting wires 8 by means of which the tube I is held in the required position with respect to the shell 4. The seals 3 of the tube are provided with cuffs 9 to which the wires 8 are spotwelded. The electrical communication between these wires and the leading-in wires of the tube is made by link-.- ing wires i0. The reflector shell 4 carries a reflecting layer 4a on the surface adjacent to the tube, and this layer is suitably produced through evaporation of aluminum. The shells 4 and 5 are firmly sealed to each other by means of the rims l2. The space between the shells is carefully evacuated through the exhaust tube I3 and filled with an inert gas the pressure. of which does not exceed a half atmosphere under operating conditions of the lamp.

In the present construction of the lamp, when the radiation is to emerge under a wide: angle. the arc of the tube is arranged in a vertical position with respect to the axis of the reflector and, consequently, about half the radiation is emitted directly, while the other half is thrown back .by the reflector. In order to give this part of the radiation a wide angle of divergence also, the arc is arranged between the reflector and its focus. The surface of the reflector shell is preferably frosted before the reflecting layer is deposited; In this case, the layer may also consist of other non-metallic materials having a high coeificient of reflection, for instance,pmagnesium oxide, which is deposited on the. surface of the shell through combustion of magnesium.

The reflector shell, which has a thickness of about 3 millimeters, consists of an ordinary glass,

which can be used also for the other shell when the lamp is to be used for illumination only. However, if the lamp is to be used for medical purposes, the shell 5 is made of a special ultraviolet transmitting glass the composition of which depends on the degree of transmission required.

' If the lamp is to be used for medical purposes. it is particularly necessary to provide. additional measures against apossible explosion of the tube, by which persons exposed to the radiation might be endangered. As indicated in Figure l, a wire screen I4 is, therefore, imbedded within the wall of the shell 5 which prevents a total destruction of this shell and stops the fragments of the exploding tube projected with great violence.

If the shell 5 consists of a so-called black glass, which in the usual way contains 3 to 6% of nickel oxide, the present lamp is excellently suited'as source for fluorescence analysis. In this case,la" smaller tube with a wattage of watts only"'is preferably used and, therefore, the lamp has a considerably smaller size. The nickel oxide glass mentioned is perfectly opaque for light at a wallthickness of 3 millimeters, while the ultra-violet radiation of the mercury arc in the spectral range of 300 to 400 mu is well transmitted.

The same construction of the lamp can be used when the light of the mercury arc is to be improved by luminescent materials. As it is known,

the light of the mercury arc contains too little" radiation in the .red and for this reason, it has been attempted to correct this defect by transforming the ultra-violet radiation, which is very considerable, into light containing a high percentage t red radiationby means, of a luminescent powder. Theoretically; a'percentage of red light corresponding to daylight and an increase luminouseiiiciency of; about should result. The efliciency of transformation of radiation through the luminescent material; however, is greatly diminished by temperature and; therefore, with lamps already known, where the'arc iscompletely surrounded by the luminescent layer, not more than one-thirdof the possible effect is obtained; The. harmful effect of temperature is avoided in the lamp shown-in Figure 1 by applying-the luminescent material as a thin layer 15 onlyonto the shell 5 which is given a larger size inorder to increase-the surface. As the lamp is operated with the pins up and the luminescent layer on-the-lower side only, the material is only to a small extent exposed to heating throughcom vection or conduction of the gas contained in the lamp. The heating effect through absorption'of .iradiation and energy losses connected with the process of transformation is relatively small. The temperature of the luminescent material produced during operation of the lamp is additionally lowered byincreasing the outer surface of the shell 5' by means of grooves or ribs. This. structure can be produced without difficulty when the shell is pressed in the mold. As luminescent materials, sulfides and silicates are-suitable. As binding. material potassium silicate or phosphoric'acid are preferably used. Both shells comprising the same glass are tightly fused to each: other bymeans of the rims after previously coating one shell. with the reflecting material and coating; the other with the luminescent layer. Theinterior space isthen carefully evacuated and the luminescent layer freed from any moisture. Preferably,'this spaceis filled with a small quantity. of oxygen, which may be also added to the usual gas-filling.

A new and efficient headlight for automobiles is obtained if, according to Figures 2 and 3, a super high pressure lamp with three electrodes having a wattage of 60 to 100 watts is used. As

shown in Figure 2, the tube is provided with. three electrodes 23, 24 and arranged symmetrically at an angle of 120 to each other and between which three mercury arcs of high brightness are formed when the electrodes are connected to three phase voltage. The distance between the electrodes amounts-to about 2 millimeters and the discharge tub has such dimensions that the pressure ofthe mercury vapor has a value of about atmospheres during operation of the lamp with the wattage indicated. The brightness of each. mercury are under these conditions amounts from 10,000 to 20,000 candles per square fcentimeter. Super high pressure lamps l with .three or more electrodes are known. However, in-this case, the'plane formed by the mercury arcs is vertically arranged with respect to the axis of the reflector and coincides with the focus.

The tubeis given such a position with respect to the reflector that the arcs formed between the electrodes 23 and 24 and between 23 and 25 produce a parallel beam of wide range, while the are formed between the electrodes 24 and 25 produces a diverging beam directedto the road. As in such multiple-electrode tubes, the arcs can be operated singly or'in pairs. It is possible in. a

simple way to use thepresent lamp as a headlight with concentrated or diverging beams by either operating the arcs 23-24 and 23-25 or 24-25 alone. This shifting from one are to another does not require a special-starting- .equipment green and yellow mercury lines.

because in. such tubes, having three; on more electrodes, each arc-is produced immediately, regardless of high pressure, when the correspond,- ing circuit is closed, provided that always atleast one are is maintained. Therefore, when this headlightlamp is tobe shifted from parallel light, e. g. when the arcs 23-24 and 23-25 are operating, to diverging light, then the are 24-25 must be first started; before the other two, are inter: rupted. Inthe reverse: case, thearcs for parallel light must be first switched on before that for diverging light is put out. Of course, the are, 24-25 can b operated permanently also, an only. the other two are started or interrupted ac cording to need. As each starting of an are re.- quires fractions of a second only, this lamp can be used'exactly in the same-way as the usual: automobile lamps having two incandescent filaments, Compared with these,v however, the :new headlight lamp ofiers extraordinary advantages as its arcs possess tentimes the brightness and three times the luminous efficiency. The light of the new lamp is reflectedby illuminated. objects to a higher degree as it is composed mainly of the For. the same reason, when' polarizing filters are used, losses through absorption are relatively small. Finally, the tube may be overloaded two or three times during short periods which results'in. a correspondingly higher candle power of the headlight. According to Figure 3, the undesirable direct emission of the tube is screened off through an auxiliary reflector 26 which produces an image of the arcs and which throws also this part of the radiation on the reflector. This auxiliary reflector is also produced by pressing in th mold as a part of the shell 5, and the metallic layer 21 is deposited, in a similar manner as with. the reflector d, by evaporation of aluminum or other metals of high coefficient of reflection. The shell 6 is provided with three base pins. The shells 4 and 5 which are made of bore-silicate glass ar fused to each other and the space enclosed by them is filled with an inert gas such as nitrogen. The blue and violet light of the mercury tube which is considerably scattered by atmospheric particles is preferably absorbed by using yellow glass in the making of the shell 5.

The small reflector lamp, according to Figures 2 and 3, is also excellently suited formi'croscopic work; in this case, a magnified'optical image of the arcs is needed, which is projected on the illuminating mirror of the miscroscope.- The tube is arranged slightly outside the focusof the reflector 4, so that the desired image is obtained nation of the microscopical field and particularly for fluorescence microscopy. This method which up to now has been little used, as" it" depended hitherto on the use of a large equipment becomes accessible toithe widest extent with the new lamp. The light'oi the mercury arc to this end is modified with an ultra-violet transmitting blue glass filter which transmits radiation below 450 mu only. If the lamp is'to be used for fluorescence microscopy only, the glass of the shell 5 is preferably coloredwith the oxides of cobalt and copper. In this case, the operation of the lamp with three phasic current is particularly advantageous as the three arcs fill out rather uniformly the space between the electrodes and in this way a source of light of nearly circular symmetry is producedwhich is required for the illumination of the microscopical object and for a uniform illumination of the field of the microscope. Also, when a tube with two electrodes only is used, the new small reflector lamp oifers extraordinary advantages due to its high brightness.

A reflector lamp of the kind described is also excellently suited as asource of light for projectors if, as in the case of the microscopical lamp, an optical image of the arc is desired at a suitable 1O distance from the lamp. As a high luminous flux is frequently required, tubes of higher wattage are used in these applications. In this case, the tube mayalso have three or even four electrodes in order to produce the circular symmetry required.

If a lamp according to Figures 2 and 3 is pro- {vided with a glass of high transmission in the ultra-violet or if quartz glass is used for the shell 5 which does not absorb ultra-violet radiation of short wave-length below 320 mu, a source of radiation is obtained which is excellently suited to germicidal uses. Compared with usual germicidal lamps, it has the advantage that small objects can be exposed to radiation from a large distance without incommodation of persons standing nearby. The new lamp, therefore, will have important uses in surgery.

A searchlight lamp, utilizing the high brightness of a super high pressure tube for the production of a parallel beam of light of very high luminous intensity, is indicated in Figures 4 and 5. In this case, the reflector forms a deep paraboloid and the arcis arranged in its focus and in a direction parallel to the axis of the reflector. The reflector shell is provided with a specular layer and, therefore, is not frosted the same Way as the other shell. In the example shown, the/ tube is supplied with an auxiliary electrode 3! which greatly facilitates the starting of the lamp. With its help, the arc can be started in such cases when the tube is hot and possesses high vapor pressure. To this end, however, a Tesla voltage of several thousand volts must be applied to the starting electrode which is supplied by a trans- ,45 former of sunicient capacity. The insulation of the customary base, however, and of the corresponding lamp-holder is not sufficient for this high voltage. The contacts of the lamp are, therefore, preferably arranged on the rims with which the shells are fused to each other. As shown in Figures 4 and 5, four contact elements 32, 33, 34 and 35 which are insulated from each other, and which consist of metal sheets with a U-shaped profile, are fastened to the rims I2. The metal sheets are flrmly connected to the lamp by pressing of each sheet into grooves specially provided in the rims, or by cementing. Each contact carries a pin 36 which, as in the usual swan-base, fits into a corresponding slot of the lamp-holder not shown in the drawing. The reflector shell 4 is not provided with basepins as the conductors emerging from the interior of the container are preferably sealed between the rims of the shells. Through this new construction of the lamp, a'method of supporting the tube results whichis different from the method already described. As shown in Figure 4, the support wires 8 carrying the tube are fastened to a plate 31, which consists of an insulating material and which is firmly connected to the reflector shell by means of a screw 38. A cap 39 is fused to the shell which is provided with a screw thread for holding the screw. To the supporting wires 8 are connected the conductors 40 and M 10 which lead, along the surface of the shell, to the seals 42 and 43 and to the contacts 32 and 33. These conductors have the form of a wire .or of a ribbon and they must be insulated against the metallic layer of the reflector. The reflector shell is preferably provided with grooves into which the conductors are inserted. The rims are also provided with such grooves, which are arranged in the planes of contact and contain the seals 42 and 43. The shells arefused to each other with the rims, in a way already described, and in this manner the leading-in Wires 42 and 63 are embedded tightly, or, if the rims cannot be fused together, they are firmly connected to each other by means of the contact elements. The starting electrode 3!, for reasons of insulation, is not connected to the contacts 33 or 35 in the same manner but its conducting wire is preferably passed across the space enclosed by the container to the rims. In order to avoid any contact with the reflectinglayer, the conductors i6 and 4| may be arranged in the same way. 7

As the maximum of luminous intensity of the arc is in the direction vertical to the axis and to the axis of the reflector, while it becomes a minimum in the direction of the arc, the supporting plate 31 absorbs only little light and asmall fraction only of the radiation can leave the lamp directly. If not wanted, this radiation may be eliminated through a shield M.

This lamp can be used as searchlight both with light or ultra-violet or infra-red radiation and the shell 5 depending on the application intended, consists of glasses with corresponding spectral transmissions. For these 7 spectral ranges, the super high pressure'arcs in krypton or Xenon, already mentioned above, are particularly efficient sources of radiation. There fore, in certain cases, one of these super high pressure tubes is used in the place of the mercury tube. These arcs, moreover, emit under high currents a nearly continuous spectrum extending from the ultra-violet'to the-infra-red, which is emitted with high radiant efiiciency. -'As :the time required for the building up and decay is very small, these arcs are particularly adapted to the operation with single or periodically repeated condenser discharges of very short duration and very high instantaneous currents. These lamps, therefore, are excellently suited for stroboscopes and as flashlights for photography with visible, ultra-violet or infra-red radiations. Due to their new design, they possess high optical efiiciencv and a particularly convenient construction.

What I claim is:

1. A gaseous discharge lamp with auxiliary envelope, comprising in combination a super hi h pressure discharge lamp having a substantially spherical quartz glass discharge vessel containing a plurality of closely spaced electrodes for operating under a pressure of more than 20 atmospheres, said discharge vessel being supported within an auxiliary envelope formed of a paraboloid reflector section and a light transmissive section, said sections being formed of molded glass and being firmly connected to each other at the rims thereof, said reflector section having at least one aperture formed therethrough, a substantially tubular and cylindrical metallic member seated in and fused to the walls of said aperture, a supporting structure for said lamp, said supporting structure being secured to said reflector section by means of said tubular metallic member, said lamp supporting structure comprising a pair of electrically conductive rods electrically connected across said'lamp.

2. A gaseous dischargelamp according to claim '1, wherein the light transmissive section is reinforced by a wire screen and the reflector section is covered with 'a metallic reflecting surface deposited by evaporation of a'm'etal of high reflectance. 5

3. A gaseous discharge lamp according to'claim 1, wherein the auxiliary envelope has a reflector section with an 'innersurface of frosted glass and a'metallic reflecting surface deposited thereonbyevaporationof a metal of 'high reflectance.

4. Agaseous-discharge lamp according'to claim 1, wherein'the auxiliary envelope has-"a reflector section with an inner surface covered with a reflecting surface consisting "of magnesium oxide deposited on said inner surface by the combustion of magnesium.

5. A gaseous discharge lamp with auxiliary envelope, comprising in combination a super high pressure discharge lamp having a substantially spherical quartz glass discharge vessel containing a plurality of closely spaced electrodes for operating under a pressure of more than 20 atmospheres, said discharge vessel being supported Within'an auxiliary envelope formed of a paraboloid reflector section and a' light transmissive section, said sections being formedof molded glass and being firmly connected to each other at the rims thereof, said reflector section having at least one aperture formed therethrough, a substantially tubular 'and cylindrical metallic member-seated in and fused to the walls of said aperture, a supporting structure for said lamp,

said supporting structure being secured to said reflectorsection'by means of said tubular metallic member, said'lamp supporting structure compr'isin'ga pair of electrically 'conductive'ro'ds electrically connected across "said lamp, electrical contacts positioned on the perimeter of said auxiliary envelope, electrical conductors for said contacts sealed between the said sectionsand leading along the inner surface of said reflector section to said rods.

6.-A metal vapor' arc di'scharge lamp accordin'g to claim 5, wherein said contacts are U-'-shaped metal sheets laid around and pressed "onto "the rims of said auxiliary envelope.

7. 'A gaseous discharge lamp "ac'cording to claim 5, wherein said discharge vessel contains three electrodes of which two are arranged to sustain an arc across the focusto produce a parallel beam or light and "the third {electrode is arranged to sustainan are outside the focus to produce a diverging beam of light.

8. Agaseous discharge lamp according to claim 5, wherein said light transmissive section contains 'an auxiliary reflector on the centr'al inner portion thereof.

9. Agaseous discharge lamp according'toclaim ,5, wherein said-arc vessel contains at least {two electrodes 'arranged outside of thefocus o'f'the reflector section to magnify an arc image at a short'distancefrom the light transmissive section.

EDUARD REFERENCES "CITED The following references are of record in the file of this patent:

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